Performance of a high-pressure xenon ionization chamber for environmental radiation monitoring

High-pressure xenon (HPXe) ionization chambers are ideal for use in uncontrolled environments, as a detector's response has been shown to be uniform over large temperature ranges (20 - 170 ^{{ring operator}} C). A cylindrical HPXe ionization chamber, which was configured with a shielding mesh to improve its energy resolution, was designed on the basis of an EGSnrc simulation code to extract an optimal density of Xe gas and a thickness of the chamber's wall. A Garfield, which was coupled with a Maxwell electric field calculator, was also employed for the electron drift simulations due to the geometry of the adapted shielding mesh. Shielding inefficiency was also calculated. A spherical ionization chamber was also designed to monitor an environmental radiation level and the responses for low dose rates with the fabricated HPXe ionization chamber were compared. A noble gas system was constructed to create a noble gas with a high purity and to inject the noble gas at up to 60 atm. The combination of an oxisorb, a molecular sieve, and a high-temperature getter can minimize the electro-negative impurities, such as the O₂ and N₂ gas, to below about several ppb levels. Preliminary tests such as leakage currents, saturation currents, and gas leak tests were performed. The performance of the two fabricated ionization chambers at a low dose rate was tested by using a conventional shadow technique with a NIST certified 0.906 mCi ²²⁶Ra standard source in a calibration room at KAERI.